Brand Finance, the corporate advisory group, says the value of the US brand has fallen 10pc since April to $11.4 trillion.

This still means the US brand is the most valuable in the world, reflecting its position as the world's biggest economy, but it has been severely damaged by inflation, higher unemployment and a declining image in the rest of the world.

The analysis, which is based on a "detailed analysis of economic data, perceptual market research data and infrastructure measures" follows comments last week from Sir Martin Sorrell, boss of the world's biggest advertising agency WPP, that the US did not realise the damage done by the Standard & Poor's downgrade.

Sir Martin said: "I don't think Americans understand how significant a dent [it has put] in its reputation around the world."

David Haigh, chief executive of Brand Finance, added: "Brand USA is under enormous pressure as a decade of crises in business and foreign policy have been joined by serious economic problems. Low consumer spending, a static property market and the sovereign debt credit downgrade have all taken their toll on the value of Brand USA."